Definetly, Objective c is the main language forn the iOS apple devices, i am also well interested in the learning of Objective C but i still am working on C to better undertstand Object oriented Languages.
I agree with Chris, you really do need to learn obj-c and cocoa if you want to develop for Mac.
My training was initially in Basic, C, C++, Pascal, VB, and a small amount of Intel Assembler. Obj-c is quite different and initially I was a bit reluctant to adapt and tried the Mono with CocoaSharp, but didn't like the process of wrapping C# to get things working. I'd recommend that approach if you needed a temporary solution to migrate C# code to the Apple platform but its more of a bandage solution.
You will grow to love the Xcode environment, Obj-c, Cocoa, and interface Builder as developing code is very quick once you understand the class libraries you need.
You might end up switching to GNUstep for development on your Windows machines as a result.